This invention relates to pressure measuring apparatus and, more specifically to a Wheatstone bridge with electrolytic resistances for measuring pressure within bodily cavities and passageways, and the like.
There are many reasons for measuring pressure within bodily cavities and passageways. Illustratively, the muscular action of the esophagus in conveying food from the mouth to the stomach, frequently referred to as gastric motility, is a matter of major medical interest. The action of the esophagus in transferring bites of food from the mouth to the stomach can be likened to a pump in which a "valve" in the throat (the crycopharyngeal sphincter) cooperates with the longitudinal and circumferential muscles associated with the esophagus and another "valve" at the opposite end of the esophagus (the distal esophageal sphincter, or D.E.S.). On swallowing, the crycopharyngeal sphincter opens to pass through a food portion and then closes. A wave of relaxation in the muscles associated with the esophagus moves the food downwardly toward the stomach and, passing the D.E.S., enters the stomach. The D.E.S., in turn, should be capable of retaining the stomach contents in the stomach in all reasonable circumstances.
Stomach contents do, however, flow back into the esophagus (i.e., reflux) in some circumstances and produce "heartburn". Generally, this failure to retain the stomach contents in the stomach may be a consequence of inadequate gastric motility and failure of the D.E.S.
To diagnose esophageal problems, several techniques are available to medical science, including motility studies that require pressure measurements in the alimentary tract. Several devices have been proposed to take these important measurements. A tube, for instance, that has a closed lower end is provided with a number of longitudinally spaced side holes. This tube is lodged in the alimentary tract with the longitudinally spaced holes each in alignment with the stomach, the D.E.S. and the level of the diaphragm, respectively. Water is pumped out of each of these side holes, the pressure required to establish flow at the specific portion of the alimentary tract reflecting the muscular forces that are being measured.
This technique, developed by Drs. Harris and Winans and described in "Quantitation of Lower Esophageal Sphincter Competence", Gastroenterology, Vol. 52, No. 5, p. 773 et seq., is subject to some difficulties. For example, if the tube is not centered within the alimentary canal, the observed pressure is reduced because the leakage path through the closed esophagus is reduced on one side or the other of center. The observed data, in this circumstance, is inaccurate.